服务器返回4xx等时，读取responsebody

HttpGet.java

import java.io.*;
import java.util.*;
import java.net.*;

public class HttpGet{
    
    public static void main(String[] argbs) throws Exception{

        String url = "http://localhost:8080/";
        
        URL obj = new URL(url);
        HttpURLConnection conn = (HttpURLConnection) obj.openConnection();
        conn.setRequestProperty("Accept", "*/*");

        conn.setRequestMethod("GET");

        int responseCode = conn.getResponseCode();
        InputStream is = conn.getErrorStream(); // 如果服务器端返回的是403等等代码，要读取返回的response body，需要从这个errorstream内读取了
        if (is == null) {
            is = conn.getInputStream();
        }
        System.out.println("\nSending 'GET' request to URL : " + url);
        System.out.println("Response Code : " + responseCode);

        BufferedReader in = new BufferedReader(new InputStreamReader(is));
        String inputLine;
        StringBuffer response = new StringBuffer();

        while ((inputLine = in.readLine()) != null) {
            response.append(inputLine);
        }
        in.close();
        is.close();

        System.out.println("Response Body :\r\n" + response.toString());

    }
}